Charge-transporting thin films made of organic compounds are used as light-emitting layers and charge-injecting layers in organic electroluminescent (EL) devices. Processes for forming such charge-transporting thin films are broadly divided into dry processes such as vapor deposition and wet processes such as spin coating. On comparing dry processes and wet processes, the latter are better able to efficiently produce thin films having a high flatness over a large area. Therefore, in the field of organic electroluminescence where thin films of larger surface area are desired, thin films are often formed by wet processes.
In light of this, the inventors have developed varnishes for the formation of charge-transporting thin films, which varnishes are intended for the production, by a wet process, of charge-transporting thin films applicable to various types of electronic devices (see, for example, Patent Document 1).
However, given recent trends in the field of organic electroluminescence toward lighter, thinner and more flexible devices, substrates made of organic compounds have come to be used in place of glass substrates. These developments have led to a desire for varnishes that can be baked at lower temperatures than conventional products and which, even in such cases, give thin films having a good charge transportability.